The mounting of one object to another is often required to be dynamic in the sense of permitting dimensional changes or movement between the objects. These changes are often accommodated by a biasing member such as a spring. One particular application requiring a dynamic mounting system is in the field of electronics where heat and vibration need to be accommodated. Within the field of electronics, the mounting of heat sinks, electronic components and circuit boards is of particular importance due to the costly nature of the elements that they attach.
It is known to use captive screws to mount a heat sink to a circuit board with an electronic component such as a microchip held between the heat sink and the circuit board. Because of the nature of electronic components such as microchips, the heat produced by the microchip can be sufficiently extreme to cause expansion of the electronic component and the heat sink. Proposed solutions for providing a dynamic mounting system for heat sinks in the field of electronics include dynamic mounting systems where a near constant clamp load is applied to the microchip through biased attachment to the circuit board. Such a solution is proposed, for example, in U.S. Patent publication 2008/0056844 entitled “Floating Captive Screw.” This document teaches limiting the depth of the penetration of an attaching biased screw member that threadably engages a nut in the circuit board. The depth is controlled by the abutment of a flange on the screw when it contacts a top surface of the nut, thus providing a positive stop to further advancement of the screw. A significant problem encountered with this construction is the possibility of damage to the costly electronic components by over tightening of the screw, because it is positively engaged with the nut.
There is therefore a need in the art for a dynamic mounting system for mounting a heat sink to a circuit board in which the attaching element such as a screw cannot be over tightened, thus avoiding costly damage. There is further a need for such a mounting system which is compact and inexpensive to manufacture.